Tetrachlorostyrene and method of preparing the same



Paten te d July 21, 1942 TETRACHLOROSTYRENE METHOD F PREPARING THE SAMEArthur A. Levine and Oliver W. Cass, Niagara Falls, N. Y., assignors toE. I. du Pont de Nemours & Company, Wilmington, Del., a corporation ofDelaware No Drawing. Application March 18,1940, Serial No. 324,617

' 7 Claims. '(Cl. 260-650) Thi invention relates to the preparation ofvaluable chlorinated aromatic compounds. More particularly, it relatesto the preparation of tetrachlorostyrene from ethyltetrachlorobenzene asa starting material. The present application is a continuation-in-partof our copending application Serial No. 136,024, filed April 9, l937which is directed to the preparation of pentachlorostyrene fromethylpentachlorobenzene.

Ethyltetrachlorobenzene is readily prepared by the nuclear chlorinationof ethylbenzene. The chlorination is carried out in the absence of lightand in the presence of a chlorine carrier which is metallic iron. Thetetrachloride is separated by distillation from the dichlorides andtetrachlorides which are formed in small amounts. The product thusobtained is a mixture of the three possible isomers ofethyltetrachlorobenzene.

Our process for the preparation of tetrachlorostyrene fromethyltetrachlorobenzene involves two steps. In the first step,ethyltetrachlorobenzene is reacted' with chlorine under conditions suchthat mono-chlorethyltetrachlorobenzene is formed. In the second step,the mono-chlorethyltetrachlorobenzene is converted to tetrastyrene bysplitting off hydrogen chloride from the side chain.

Accordingly, one of the objects of this invention involves thepreparation of tetrachlorostyrene from ethyltetrachlorobenzene insatisfactory yield. Another object is the preparation of thedesiredproduct, tetrachlorostyrene, by means of a two-stageprocessinvolving two separate chemical reactions. The first of thesereactions involves the preparation 'ofmono-chlorethyltetrachlorobenzene, and the second the conversion of thatproduct to tetrachlorostyrene.

The various isomers of tetrachlorostyrene represented by the formulaCsHCh.CH =CHa are believed to be new compounds never before described inthe chemical literature. It is, therefore, a further object of thisinvention to produce these new chemical compounds. Other objects andadvantages of the invention will be apparent from the ensuing detaileddisclosure.

In order to convert ethyltetrachlorobenzene tomono-chlorethyltetrachlorobenzene, the ethyltetrachlorobenzene startingmaterial may be reacted with chlorine in the presence of light and inthe absence of any chlorine carrier until ap proximately 50% of theamount of chlorine theoretically required for the introduction of onechlorine atom per mole of ethyltetrachlorobenapproximately 50% unchangedethyltetrachloroe I benzene and 50% mono chlorethyltetrachlorobenzene.If much more than, 50% of the theo-' retical chlorine is added, theyields are decreased due to the formation of higher chlorides. Thereaction involved is represented by the following equation:

styrene. The reaction is as follows:

CeHC14.CzH4C1 CBHCI4.CH=CH2+l-IC1 Alternatively thechlorethyltetrachlorobenzene may be converted to tetrachlorostyrene bytreat-- ment of the former with a base as, for example, alcoholicpotassium hydroxide, or the removal of one molecule of HCl from thechiorethyl side chain of chlorethyltetrachlorobenzene may be effected bymeans of any of the other usual dehydrohalogenation treatments known inthe art.

The invention may be further illustrated by the specific proceduredescribed in the following example EXAMPLE Preparation ofethyltetrachlorobenzene A mixture of the isomers ofethyltetrachlorobenzene was prepared in the following manner: 636 grams(6.8 moles) of ethylbenzene was placed in a two-liter, three-neckedflask fitted with a stirrer,-a thermometer, an inlet tube for chlorineand a refiux condenser leading to a scrubbing system for absorbing theevolved hydrogen. Iron filings in the amount of 15 grams were/then addedto the fiask and operation of the stirrer begun.

Chlorine gas was then passed in and the temperature of the reactionvessel was maintained below 30 C. at all times by externally cooling theflask. The fiask and its contents were care- 1 fully screened from lightduring the hl r zene has been added. This gives a mixture of.

period. After 864 grams (28.8 moles) of hydro- Conversion ofethyltetrachlorobenzene to monochlorethyltetrachlorobenzene 732 grams (3moles) of ethyltetrachlorobenzene was charged into a reaction vesselequipped with a stirrer, a chlorine inlet tube, a thermometer, and areflux condenser leading to a hydrogen chloride trap containing water.

The reaction vessel was illuminated by means of an incandescent lamp.

The ethyltetrachlorobenzene was then heated to about IOU-110 C. and 108grams (2.52 moles) of chlorine was gradually introduced. During thecourse of the reaction, 54 grams of hydrogen chloride was evolved andthe gain in weight of the contents of the flask was approximately 51grams.

The reaction mixturewas then vacuum-distilled under an absolute pressureof 10 mm. of mercury. The portion distilling below a temperature of 150C. consisted principally of unchang'ed ethyltetrachlorobenzene.distilling between 150 and 170 C. consisted essentially of a mixture ofthe isomers of monochlorethyltetrachlorobenzene. The product had adensity of 1.523 at 50 C. and a melting point below -40 C.

Conversion of mono-chlorethyltetrachlorobenzene to tetrachlorostyreneThe mixture of mono-chlorethyltetrachlororemarkably stable material andshows no tend- The fraction ency to polymerize under the action ofeither light or heat.

Because of its stability,low melting point and other desirableproperties, tetrachlorostyrene is adapted for use either alone or incombination with other materials iorsuch varied purposes as dielectricmedia for electrical apparatus, media for transferring heat at elevatedtemperatures, brake fluids and hydraulic brake systems, extreme pressurelubricants, absorbents in scrubbing systems, cooling agents for internalcombustion engines, -etc. a

It is to be understood that our invention is not restricted to thespecific embodiments described hereinabove, but includes all suchmodifications, 4 variations, and equivalents, as fall within the scopeof the appended claims..

We claim:

1. A process for preparing tetrachlorostyrene which compriseschlorinating ethyltetrachlorobenzene to form amono-chlorethyltetrachlorobenzene and subjecting saidmono-chloroethyltetrachlorobenzene to dehydrochlorination conditions,thereby removing one mole of hydrogen chloride and formingtetrachlorostyrene.

2. A process for preparing tetrachlorostyrene which comprises reactingethyltetrachlorobenzene with chlorine in the absence of a halogenationcatalyst, but in the presence of light, to formmono-chlorethyltetrachlorobenzene and then subjecting saidmono-chlorethyltetrachlorobenzene to dehydrochlorination conditions toform tetrachlorostyrene.

3. A process of preparing tetrachlorostyrene which comprises reactingethyltetrachlorobenzene with chlorine in the absence of a halogenationcatalyst, but in the presence of light, to formmono-chlorethyltetrachlorobenzenev and then pyrolytically decomposingsaid mono-chlorethyltetrachlorobenzene to form tetrachlorostyrene.

4. A process for preparing tetrachlorostyrene frommono-chlorethyltetrachlorobenzene which comprises subjecting saidmono-chlorethyltetrachlorobenzene to dehydrochlorination conditions,thereby removing one mole of hydrogen chloride per mole ofmono-chlorethyltetrachlorobenzene. 5. A process for preparingtetrachlorostyrene which comprises subjectingmono-chlorethyltetrachlorobenzene to thermodecomposition, therebyremoving one mole of hydrogen chloride per mole ofmono-chlorethyltetrachlorobenzene.

6. Tetrachlorstyrene. 7. A composition comprising essentially mixedisomers of tetrachlorostyrene.

ARTHUR A. LEVINE. OLIVER W. CASS.

